Arrangement comprising cathode ray tubes



Dec. 23, 1941. DE GlER I 2,267,@83 ARRANGEMENT COMPRISING CATHODE RAYTUBES Filed. May 24, 1959 v TELEVISION RECE/Vl/VG APPARATUS ATTORNEYPatented Dec. 23, 1941 STATES mean eerie ARRANGEMENT COMPRISING CATHODERA Y TUBES poration of Delaware Application May 24, 1939, Serial No.275,393 In Germany June 13, 1938 3 Claims.

It has already been suggested to provide a cathode ray tube with fourapertured diaphragms having alternately a high and a low potential, andto apply modulation voltages to the first and to the third screen. Thisarrangement has the advantage that the characteristic curve of the tubemay have a desired curvature but involves the disadvantage that for eachelectrode a special voltage connection must be available.

According to the invention the apertures of the diaphragms are chosen ofdifferent. size in the case of tubes having, at least three apertureddiaphragms before the cathode, i. e., the aperture in the firstdiaphragm or electrode is larger than the aperture in the thirddiaphragm. This makes it possible to obtain a still more defined andreduced spot of light on the screen or target electrode, and, inaddition, to connect these electrodes directly one with another. If afourth apertured diaphragm or electrode is provided, this may beconnected directly to the second diaphragm or electrode. In this mannertwo connections to the supply device are avoided. The connections arepreferably arranged at the inside of the tube itself so that for thefour electrodes only two terminals of the tube are to be connected tothe supply device.

In view of the slope of the characteristic curve a. larger axialdimension is used for the third electrode than for the first one. It isalso advantageous, if the second electrode has a larger aperture thanthe fourth one. However, it is preferably chosen smaller than theaperture in the first. electrode, and the aperture in the thirddiaphragm or electrode is at the utmost equally large as the aperture inthe second electrode.

A favorable feature of the arrangement according to the inventionconsists in that the unavoidable voltage fluctuations in the availablemains circuit affect the intensity of the cathode rays to a less extentor in case of correctly chosen voltage conditions do not affect it atall practically within wide ranges.

The invention may be used for several purposes, for example, inconnection with the receiving tube of a television receiver, with tubesfor the transmission of pictures and with the cathode ray oscillograph.

In devices including the modulation of the intensity of the cathode raybeam the invention entails the advantage that a particularly favorablecurvature of the characteristic curve may be obtained and that at thesame time a great slope is possible, an advantage which is obtainedaccording to the invention with a very simple circuit arrangement.

The invention will be more clearly understood with reference to theattached drawing showing, by way of example, a form of construction ofan arrangement according to the invention.

The cathode I is surrounded by an electrode 01' Wehnelt cylinder 2 whichis connected to a point 4 at the potentiometer 5 through the resistance3. Modulation voltages may be applied to the resistance 3. The point 4has a negative potential of say 25 volts in regard to the point 6, towhich the cathode is connected. The end wall 9 of the electrode 2 isarranged in front of the emitting surface 8 of the cathode and has anaperture ID of say 2 mm. in diameter, allowing the passage of electronstherethrough. An apertured electrode II is connected to the point I2 ofthe potentiometer 5. The latter has a positive potential of say -300volts positive in regard to the cathode.

The positive electrode II, which has an aperture I3 allowing the passageof electrons of say 1.5 mm., is followed again by a negative electrodeI4 which has preferably a larger axial dimension than the electrode. 9.The aperture I5 in the screen I4 is say 1 mm. in diameter. Finally apositive apertured electrode I6 is provided, the aperture ll of whichhas a smaller diameter than the apertures of the preceding electrodes.It'is say 0.5 mm. The electrode It may be dispensed with, if the furtherpart of the tube I8 comprises another positive electrode, for example inthe form of a conducting wall coating.

A further concentration of the cathode-ray beam may be produced also bya magnetic field.

Said arrangement of the electrode system and the above-mentionedpotential division maintains the current of the cathode ray beam passingthrough the aperture I'I, independent within wide ranges of the voltageof the source feeding the device. This can be explained as follows: Aportion of the electrons emitted by the cathode is reflected by thenegative screen I4 and collected by the screen II. In case of a highervoltage at the potentiometer 5 the potential difierence between the grid9 and the cathode I is increased, involving a decrease of the beamcurrent. If the reflection of electrons to the electrode II increasesdue to the decrease of the potential at the screen I4, the potential ofII and It increases to a less extent than the terminal voltage due tothe voltage drop in the part of the potentiometer 5 traversed bycurrent, or it may even decrease. In this casethedecrease of thepotential of the electrode 9 is not compensated for by a higher anodevoltage. The arrangement according to the invention does not show thiseffect; in this arrangement the deflection of electrons to the electrodeII does not increase with a decrease of the potential of the electrodeI4. If the aperture I3 is larger than the aperture I5, the current ofelectrons absorbed by the electrode ll may even decrease at a highernegative voltage of the grid Hi. If the potential of the controlelectrode 9 becomes more negative due to an increase of the mainsvoltage, the decrease in current involved is compensated for by theincrease of voltage at the electrodes l I and H5 in case of correctdimensions of the electrode apertures. The feed device may therefore beconstructed for a comparatively low current capacity, for the voltagedrop interferes only to a small degree.

In spite of the independency of the beam current with respect to thevariations of the grid voltage produced by variation of the mainsvoltage, the tube has a considerable slope.

In cathode ray tubes with electrostatically modulated beam current theratio between current and modulation voltage may be expressed by theformula I=kE in which I is the current of the beam of rays and E themodulation voltage. The larger the exponent p, the more thecharacteristic curve of the tube is curved and the sharper becomes thepicture.

With a picture film the ratio between the blackening S and thebrightness B of the recorded object is given by a corresponding formulaS=lB If the electrical transmission of films is concerned, the exponentp of which has a value of approximately 1.8, a Braun tube with constantslope (12:1) may be used for the projection. For the reproduction of adirectly recorded picture, the tube itself has to produce the curvatureof the brightness curve of the picture and p is to be given preferablythe value 1.8. This may be accomplished, as is known, by providing twomodulation electrods which are alternating with a positive electrode. Inthe known arrangement the two modulation electrodes must have differentground potential and unequally high modulation voltages. For thispurpose special potentiometers and connection means are required. Theinvention makes the several voltages superfluous. In View of the factthat the aperture H! of the first control electrode 9 is taken largerthan the aperture ii of the control electrode M, the characteristiccurve is formed such that it corresponds to the desired equation atequal potential of the electrodes 9 and Id. In order to assure that thefactor k is suificiently great, without increasing the internalresistance of the tube, a larger axial dimension is used for the second.modulation electrode it than for the first one 9. This electrode may be,for example, two times as thick as the electrode 9.

Besides the advantage that in the arrangement according to the inventionthe variation of the light intensity due to variations of voltage isonly very small, the invention entails the advantage of a very goodpicture quality with an excellent slope.

The electrode system is surrounded by a cylindrical electrode l9. Thisserves for shielding the electrode system and accordingly makes thecontrol system insensitive with respect to extraneous electric fields.It simplifies also the arrangement of the electrodes, since the positiveelectrodes ll and I6 may be directly connected electrically to theshield so as to permit the use of the shield at the same time as asupport for the electrodes H and I6. If the distance between theelectrodes is sufiiciently small, or if the outer diameters thereof aresufficiently large, the shield I9 is superfluous and may be omitted.

The electrode arrangement shown in the drawing and described above maybe very advantageously applied to the image tube in a televisionreceiving set. A television receiving apparatus is shown schematicallyat 29, the amplified and detected video signals being impressed acrossthe resistance 3 in order to modulate the cathode ray beam in the mannerexplained above. The cathode ray beam may be appropriately deflected byelectrostatic and/or electromagnetic means in order to scan thefluorescent or luminescent coating 22 on the inside surface of theenlarged end of the cathode ray tube. The intensity of the cathode raybeam as determined by the modulating potentials applied thereto,together with the systematic deflection of the beam over the fiuorescentmaterial 22, causes a reproduction of a television image. In suchdevices it is highly desirable that the intensity and focus of thecathode ray beam be not affected by variations in the power supply, andthe device shown and described will overcome any such variations so thatthe intensity of the cathode ray beam will depend solely upon themodulating potentials derived from the television receiving apparatusand not upon variations in the source of voltage supply. Furthermore,the cathode ray beam will remain in proper focus irrespective of slightchanges in the voltage at the power supply by reason of the arrangementin accordance with the present invention.

It is obvious that various alterations and modifications may be made inthe present invention and that the device disclosed may be used invarious capacities without departing from the spirit and scope of theinvention, and it is desired that any and all such modifications andusages be considered within the purview of the present invention exceptas limited by the hereinafter appended claims.

I claim:

1. A cathode ray tube including a source of electrons for producing acathode ray beam and a plurality of electrodes for determining theintensity of the beam and for controlling the crosssectional area orfocus of the beam, said plurality of electrodes including a firstcontrol electrode,

maintaining said control electrodes normally negative with respect tosaid source of electrons,

means for electrically connecting said accelerating electrodes to saidtubular shield member, and means including said source of potential formaintaining said accelerating electrodes and said tubular memberpositive with respect to said source of electrons whereby variations inthe beam current as well as the focus of the beam are unafiected bychanges in the source of potential.

2. In combination with a television receiving apparatus wherein meansare provided for receiving and amplifying television signals, a cathoderay tube including a cathode for producing a beam of electrons and afluorescent or luminescent screen against which the electrons aredirected, aplurality of electrodes including a first control electrode,an accelerating electrode and a second control electrode, all of saidelectrodes being positioned between said cathode and the screen andrelatively adjacent the cathode, each of the electrodes being providedwith a circular aperture, the apertures being in axial alignment and ofdecreasing diameter in the direction of electron beam flow, a source ofpotential, a potentiometer connected across said source of potential,means including said potentiometer for maintaining said controlelectrodes negative with respect to said cathode by a predeterminedamount, a tubular member surrounding all of said electrodes forshielding said electrodes, means for connecting said tubular shieldmember to said accelerating electrode, means including saidpotentiometer for maintaining said accelerating electrode and saidtubular shield member positive with respect to said cathode, and meansfor impressing the television signals across the control electrode andthe cathode,

whereby the intensity of the cathode ray beam may be varied inaccordance with the television signals, and whereby variations in thebeam intensity and the focus of the beam will be independent ofvariations in the source of potential. 3. A cathode ray tube including acathode for producing a cathode ray beam and a plurality of electrodesfor determining the intensity of the beam and for controlling thecross-sectional area thereof, said plurality of electrodes including afirst control electrode, a first accelerating electrode, a secondcontrol electrode and a second accelerating electrode, the electrodesbeing positioned in the order named, and the control electrodes and theaccelerating electrodes being provided with axially aligned apertures ofprogressively decreasing size in the direction of electron beam flow,means for normally maintaining the control electrodes negative withrespect to the cathode by a predetermined like amount, a tubular membersurrounding all of said electrodes for shielding said electrodes, meansfor electrically connecting the said tubular shield member to saidaccelerating electrodes, and means for maintaining the acceleratingelectrodes and the tubular shield electrode positive with respect to thecathode by a predetermined like amount.

JOI-IANNES DE GIER.

